Please note, this antenna is already included with each sensor already. Only purchase this as an original direct replacement if you lose or break it. It's necessary only if the current one malfunctions, gets lost, or becomes inoperable. Looking for high performance? Try our upgraded antennas or cable extensions if you're looking for additional performance. 18 inches length (0.5m) Magnetic base MCX connector (fits your sensor) < 5mm in diameter (squeeze through most holes in safes)